The phosphine derivative according to the present invention is an important reactant widely used for an organic synthesis reaction such as Wittig reaction or Mitsunobu reaction. In these reactions, phosphine oxide derivatives are generated as a by-product and stored in a repository or the like in large quantities as an intractable waste. If the phosphine oxide derivatives can be reduced by an appropriate method, to convert the derivatives to phosphine derivatives, it allows the regeneration and recycle of the reactant and clears up the disposal problem of the intractable waste described above once for all.
As a reaction example that converts a phosphine oxide derivative to a phosphine derivative, methods where a metal hydride is allowed to act (NON-PATENT DOCUMENT 5) such as a reaction using trichlorosilane as shown by the following equation (3) (NON-PATENT DOCUMENT 1), a reaction using triethoxysilane or polymethylhydrosiloxane as shown by the following equation (4) (NON-PATENT DOCUMENT 2), a reaction using lithium aluminum hydride and cerium chloride as shown by the following equation (5) (NON-PATENT DOCUMENT 3), a reaction using lithium aluminum hydride as shown by the following equation (6) (NON-PATENT DOCUMENT 4), and a reaction using alane as shown by the following equation (7) are reported.

However, these metal hydrides are all expensive and involve the risk of ignition or the like, and thus extra care is required for handling. Therefore, there is a problem in treating large quantities of phosphine oxide derivatives, from the viewpoint of cost, complex operations and the like.
As another reduction reaction of a triphenylphosphine oxide, a reaction where magnesium metal and titanocene dichloride are allowed to act as shown by the following equation (8) (NON-PATENT DOCUMENT 6), a reaction where samarium iodide is allowed to act as shown by the following equation (9) (NON-PATENT DOCUMENT 7), a reaction where activated carbon and hydrocarbon are allowed to act as shown by the following equation (10) (PATENT DOCUMENT 1), a reaction where a reductant prepared from a bismuth oxide and a titanium oxide is allowed to act as shown by the following equation (11) (PATENT DOCUMENT 2), a reaction where light is allowed to act in the presence of a titanium oxide as shown by the following equation (12) (NON-PATENT DOCUMENT 8), a reaction where silicon powder, chlorosilane, and iron chloride are allowed to act as shown by the following equation (13) (PATENT DOCUMENT 3), and the like are reported. However, these reactions can never be said as a practical method of producing triphenylphosphine, from the viewpoint of cost and safety.

In addition, as for electrolytic reduction of triphenylphosphine oxide, a reaction shown by the following equation (14) (PATENT DOCUMENT 4) is reported.

However, the product is a complex mixture of benzene, cyclohexadiene, cyclohexene, and the like, in addition to diphenylphosphine oxide, phenylphosphine, and diphenylphosphine, and triphenylphosphine is not produced at all.
Furthermore, a method of subjecting triphenylphosphine oxide to electrolytic reduction in acetonitrile in the presence of aluminum chloride using aluminum as an anode to produce triphenylphosphine as shown by the following equation (15) (PATENT DOCUMENT 5 and NON-PATENT DOCUMENT 9), a method of treating a triphenylphosphine oxide derivative with phosphorus pentasulfide and dimethyl sulfate, and thereafter carrying out electrolytic reduction in methanol containing lithium chloride to produce triphenylphosphine as shown by the following equation (16), and a method of treating with methyl trifluoromethanesulfonate, and thereafter carrying out electrolytic reduction in methanol containing tetrabutylammonium trifluoromethanesulfonate to produce triphenylphosphine (PATENT DOCUMENT 10) are reported. However, in the former, the yield of triphenylphosphine is only 11%, and the current efficiency is also 8% or less, and thus it can never be said as a technology for practical use. Also, in the latter, complex operations are necessary for the preparation of a pentavalent phosphorus compound to be subjected to electrolysis, and the yield of the total process including electrolytic reduction is at most 45% or so, and thus it is not satisfactory as a practical method.

On the other hand, as a two-step method including the steps of once converting triphenylphosphine oxide to one other pentavalent phosphorus compound and reducing this compound to convert the compound to triphenylphosphine, the following equation (17) is reported (NON-PATENT DOCUMENT 11). However, expensive lithium aluminum hydride is used in the reduction reaction of the second step, and thus it is not practical.

In addition, a method of synthesizing triphenylphosphine represented by the following formula (2) (Ar is a phenyl group) in high yield by a reaction where lithium aluminum hydride or sodium metal is allowed to act on a pentavalent phosphorus compound represented by the following formula (18) (Ar is a phenyl group, X is chlorine) prepared from triphenylphosphine oxide represented by the following formula (1) (Ar is a phenyl group), as shown by the following equation (19), is reported (NON-PATENT DOCUMENT 12).

However, this reaction involves the risk of ignition or the like and uses lithium aluminum hydride or sodium metal that requires extra care for handling, and thus there are many problems as a practical method that treats large quantities of triphenylphosphine oxides.
In addition, as a method of synthesizing triphenylphosphine represented by the following formula (2) from a pentavalent phosphorus compound represented by the following formula (18) (Ar is a phenyl group, X is chlorine), a method where thiophenol is allowed to act as shown by the following equation (20) (NON-PATENT DOCUMENT 13), a method where butyllithium is allowed to act as shown by the following equation (21) (NON-PATENT DOCUMENT 14), a method where phenylmagnesium bromide is allowed to act as shown by the following equation (22) (NON-PATENT DOCUMENT 14), a method where white phosphorus is allowed to act as shown by the following equation (23) (PATENT DOCUMENT 6), a method where silicon powder is allowed to act as shown by the following equation (24) (PATENT DOCUMENT 7), a method where iron powder is allowed to act as shown by the following equation (25) (PATENT DOCUMENT 8), a method where sodium metal and phosphorus trichloride are allowed to act as shown by the following equation (26) (PATENT DOCUMENT 9), and methods such as hydrogenation reactions as shown by the following equations (27) to (32) (PATENT DOCUMENTS 10 to 15) are reported. However, all methods require an expensive reactant in excess amount, strict reaction conditions of high temperature and high pressure or the like, and thus these methods are not fully satisfied as a practical method of reducing the pentavalent phosphorus compound represented by the following formula (18) for practical use.

Also, methods of synthesizing triphenylphosphine represented by the following formula (2) (Ar is a phenyl group) in high yield by reactions where aluminum metal is allowed to act on a pentavalent phosphorus compound represented by the following formula (18) (Ar is a phenyl group, X is chlorine) prepared from triphenylphosphine oxide represented by the following formula (1) (Ar is a phenyl group), as shown by the following equations (33) to (35) are reported (PATENT DOCUMENTS 16 to 18). However, these production methods are all carried out under the reaction conditions of a high temperature at 90° to 180° C., and many methods take a long treatment time of several hours to 20 hours. Aluminum used is preferably in powder form, and those previously made uniform to a proper range of particle diameter (200 to 500 μm) by a sieve are advantageously used. However, not only this adjustment costs much, but also, aluminum in powder form is easy to ignite, and thus extra care is required for handling. In addition, the pentavalent phosphorus compound represented by the following formula (18) (Ar is a phenyl group, X is chlorine) to be subjected to the reaction is prepared by reacting triphenylphosphine oxide with a chlorinating agent such as phosgene, and normally, separation and purification operations are necessary after the reaction, and it is required that the chlorinating agent and a chlorination product generated as a by-product are reduced to within the limits. The reported method of producing a phosphine derivative by the preparation of the pentavalent phosphorus compound represented by the following formula (18) (Ar is a phenyl group, X is chlorine) from a phosphine oxide derivative and the reduction by aluminum metal is not fully satisfactory as a practical method, and the development of the production method suitable for industrialization is anticipated.
